This puzzle:

JimH notes: As the long answer at 7 Down implies, there are ten symmetrically arranged Across answers which need the word DOG added to make sense. 1 Across is HOT DOG, 9 is DEVIL DOG, 15 is ALPHA DOG, 36 is DOG EAR, 34 is DOG CATCHER. Those are all in the top half. Rotating the grid to see the symmetric answers in the bottom half you get DOG TAG, DOG BREEDER, LUCKY DOG, SALTY DOG, and at 74 across you need to add the missing word twice to get DOG EAT DOG.